Honey-it doesn't seem inconsiderate, it IS inconsiderate, to both women.
But yes-I concur and I'm so sorry you had to suffer that as well!
We as people need to really put some time and effort into considering the long term potential consequences of our actions-which it sounds like he isn't.
see if you can get your hands on the book Opening Up at a used book store (always cheaper that way).
It has a GREAT list of "things to consider when making a boundary list in an open relationship".
We found it VERY eye-opening and VERY VERY helpful! I think we've avoided a LOT of issues we would have struggled through unwittingly simply becuase of that book.